earth sci

• Diastrophism


  Dynamic internal forces that tend to cause the earth's surface to undergo deformation
• Tectonic movement


  Creates tremendous stress near plate boundaries
• Stress


  Deforms rocks
• Rocks


  • React to stress by deforming elastically by a slight amount initially
  • Near Earth's surface, different types of rocks behave differently with continuing stress
• Brittle fracture


  Rocks fail by shattering (e.g. quartz)
• Plastic deformation


  Rocks deform and stay deformed (e.g. gold nugget)
• Elastic deformation


  Rocks deform and rebound immediately (e.g. rubber ball)
• Temperature


  The higher the temperature, the greater the tendency of a rock to deform in a plastic manner
• Pressure


  High non-directed (hydrostatic) pressure favors plastic behavior
• Burial


  Increases temperature and pressure, promoting plastic deformation in deeply buried rocks
• Stress applied slowly


  Favors plastic behavior
• Stress applied rapidly


  Causes brittle fracture
• Conditions for deformation


  • Rock material must have ability to deform under pressure and heat
  • Higher temperature makes rock more elastic
  • Pressure must not exceed internal strength, otherwise fracturing occurs
  • Deformation must be applied slowly
• Types of geologic structures

  • Folds
  • Faults
  • Joints
• Fold


  A bend in rock, formed by ductile deformation
• Characteristics of folds


  • Folding usually results from compression
  • Folding always shortens the horizontal distances in rock
  • A fold usually occurs as part of a group of many similar folds
• Anticline


  A fold arching upward
• Syncline


  A fold arching downward
• Dome


  A circular or elliptical anticlinal structure
• Basin


  A similarly shaped syncline
• Monocline


  An open, step-like structure in which the layers are all inclined in the same direction on either side of the fold axis
• Fault


  A fracture along which rock on one side moved relative to rock on the other side
• Tectonic forces


  Commonly persist in the same place over long periods of time
• Normal fault


  Forms where tectonic movement stretches Earth's crust, pulling it apart
• Reverse fault


  Forms where compressive forces fracture the rock, with the hanging wall moving upward relative to the footwall
• Strike-slip fault


  A vertical or nearly vertical fracture where rocks on opposite sides move horizontally past each other
• Transform plate boundary


  A strike-slip fault
• Joint


  A fracture in which rocks on either side have not moved
• Plate boundaries


  Produce different tectonic structures: divergent, transform, or convergent
• Strike-slip fault


  If the side across the fault moves to the left, it is a left-lateral strike-slip fault
• San Andreas Fault


  A zone of strike-slip faults that form the boundary between the Pacific plate and the North American plate
• Joints


  • Tectonic forces create them
  • Most rocks near Earth's surface are jointed
  • Become less abundant with depth because rocks become more plastic and less prone to fracturing
• Plate boundaries


  • Divergent - stretching adjacent rock and producing normal faults and grabens but little folding of rocks
  • Transform - friction often holds rock together as the plates gradually slip past each other, resulting in folding, faulting, and uplift
  • Convergent - compression commonly produces large regions of folds, reverse faults, and thrust faults
• Shortly after World War II, scientists began to explore the floors of Earth's oceans
• Mid-Oceanic Ridge


  The largest mountain chain on Earth, lying directly in the middle of the Atlantic Ocean, halfway between North and South America to the west, and Europe and Africa to the East
• Oldest rocks


  The rock at the far left and far right (rock that has spread the farthest) of the Mid-Atlantic Ridge
• Youngest rocks


  The rocks immediately adjacent to the Mid-Atlantic Ridge
• Oceanic crust is composed mostly of basalt, an igneous rock rich in iron
• As basaltic lava cools and becomes solid rock, the iron-rich minerals become weak magnets that align their magnetic fields parallel to Earth's magnetic field
• Oceanographers towed devices called magnetometers behind their research vessels to detect and record magnetic patterns in the deep oceans